(1) Field of the Invention
The invention relates to a fast switching continuous time CMOS comparator with dynamic biasing circuit, and more particularly, to a continuous time comparator having a dynamic biasing circuit which self-adjusts the biasing current, depending on the voltage difference of the two input signals of the comparator, in order to draw high biasing current only when required and still maintaining overall low power consumption.
(2) Description of the Prior Art
Continuous time CMOS comparators use high bias currents to achieve high speed switching characteristics. Since it is unknown when the switching point is being reached, bias current is always left at its high level, causing high overall power consumption.
Several patents describe the use of dynamic or adaptive or self-adjusting bias currents, however, none of them uses such an adaptive method to get high bias currents at the time when switching is likely to happen and to reduce said bias current at other times.
U.S. Pat. No. 6,204,654 (Miranda, et al.) dicloses a dynamically boosted current source circuit to improve the response speed of a circuit responsive to a transitioning input signal. A threshold detector detects the occurrence of an input signal transition prior to its detection by the responsive circuit, and triggers the current source to provide the boosted current; this improves the responsive circuit's speed. The current source provides the boosted current for a predetermined time interval, or until the input signal crosses a second threshold, enabling response speed to be increased without a significant increase in supply current.
U.S. Pat. No. 5,471,171 (to Itakura, et al.) describes an amplifier device capable of realizing high slew rate with low power consumption. It includes a determination element for determining a change condition of the level change of the input signal to generate a control signal corresponding to said change condition and a driving capability increase element as a circuit for increasing a bias current, depending on said change condition, in order to increase the driving output supplied.
U.S. Pat. No. 6,239,658 (to Tham) shows a control circuit, which is used to increase the DC, current of a low noise amplifier for a mobile wireless communication system in the presence of jamming signal to preserve high dynamic range. The difference signal between the input signal with jamming signal and the average input is detected by a peak detector.
The following articles discuss subjects close to the invention:
“Adaptive Biasing CMOS Amplifiers”, (Degrauwe, Rijmenants, Vittoz and De Man, IEEE Journal of Solid-State Circuits, Vol SC-17, No. 3 Jun. 1982 pp 887) discusses two transconductance amplifiers in which the concept of an input dependent bias current is introduced.
“Dynamic CMOS Amplifiers”, (Hosticka, IEEE Journal of Solid-State Circuits, Vol SC-15, No. 5 Oct. 1980, pp 522) presents the concept of dynamic amplifiers with different biasing principles.